1. Field of the Invention
The present invention relates to an apparatus for producing trichlorosilane and a method for producing trichlorosilane by converting silicon tetrachloride to trichlorosilane.
Priority is claimed on Japanese Patent Application No. 2010-047958 filed Mar. 4, 2010, the content of which is incorporated herein by reference.
2. Description of Related Art
Trichlorosilane (SiHCl3) is used as a raw material for producing silicon (Si). The trichlorosilane can be produced by conversion of silicon tetrachloride (SiCl4) through a reaction of silicon tetrachloride and hydrogen.
Silicon is produced by reductive reaction and thermolysis reaction of trichlorosilane shown by the below-described reaction formulae (1) and (2), and trichlorosilane is produced by the conversion reaction shown by the below-described reaction formula (3).SiHCl3+H2→Si+3HCl  (1)4SiHCl3→Si+3SiCl4+2H2  (2)SiCl4+H2→SiHCl3HCl  (3)
For example, as an apparatus for producing trichlorosilane, Japanese Patent No. 3781439 and Japanese Unexamined Patent Application, First Publication, No. 2004-262753 propose a reaction vessel having a reaction chamber of dual structure constituted of outer chamber and inner chamber formed by two pipes of concentric alignment, and a heating element disposed to surround outer circumference of the reaction chamber. In this reaction vessel, reaction of a gas in the reaction chamber is caused by heating the interior of the reaction chamber from the outside by the heat generated by electrifying the heating element formed of carbon or the like.
Japanese Examined Patent Application, Second Publication No. S60-49021 discloses an apparatus in which a plurality of pipe-shaped heaters are disposed inside the reaction chamber, and a gas is directly heated in the reaction chamber and within the heaters.
A lower space of a reaction chamber tends to have low temperature. Japanese Unexamined Patent Application, First Publication No. 2007-3129 proposes a heater wherein a thickness of the heater is changed in the intermediate position to reduce a cross sectional area of a lower portion of the heater such that high temperature heat is generated in the lower portion of the heater thereby heating the lower space of the reaction chamber effectively.
In general, in an apparatus for producing trichlorosilane, carbon members coated with silicon carbide are used in reaction vessel and heaters so as to prevent generation of impurities at high temperature. In an apparatus for producing trichlorosilane, it is required to heat the interior of the reaction chamber to a reaction temperature of trichlorosilane at high heat efficiency. On the other hand, where the heater is heated to excessively high temperature, damage may be caused in the silicon carbide coating on the surface of the heater, resulting in exposure of carbon and generation of impurities from the carbon. Therefore, it is required to increase high temperature area of the surface of the heater while maintaining a maximum temperature of the surface of the heater to be not higher than an upper limit.
Where an apparatus has a structure as described in Japanese Patent No. 3781439 or in Japanese Unexamined Patent Application, First Publication No. 2004-262753, interior of the reaction chamber is heated by the heating element disposed outside the reaction chamber. In this case, heat from the heating element is radiated not only in the inner radial direction but also in the outer radial direction, resulting in a disadvantage of
Although the heaters are disposed in the reaction chamber in the apparatus described in Japanese Examined Patent Application, Second Publication No. S60-49021, the constitution of the apparatus is not efficient since the gas passes through narrow pipes.
In the heater described in Japanese Unexamined Patent Application, First Publication No. 2007-3129, power density of the lower portion of the heater is increased by making the cross-sectional area of the lower portion of the heater to be smaller than the cross-sectional area of the upper portion of the heater. However, upper portion of the heater must have remarkably large size so as to decrease power density of the upper portion largely while having the heater stand stably by ensuring sufficient cross sectional area for the lower portion of the heater. In this constitution, there is a possibility of restriction of numbers and/or arrangement of the heaters when a plurality of heaters are disposed in a reaction chamber.
Based on the consideration of the above-described problems, an object of the present invention is to provide an apparatus for producing trichlorosilane and a method for producing trichlorosilane that enable heating of raw gas at improved high heat efficiency while controlling the maximum temperature of the surface of the heater in the reaction chamber.